Trypanosome trans-sialidase mediates neuroprotection against oxidative stress, serum/glucose deprivation, and hypoxia-induced neurite retraction in Trk-expressing PC12 cells

Novel Therapeutic Target Critical for SARS-CoV-2 Infectivity and Induction of the Cytokine Release Syndrome

We discovered a novel therapeutic target critical for SARS-CoV-2, cellular infectivity and the induction of the cytokine release syndrome. Here, we show that the mammalian enzyme neuraminidase-1 (Neu-1) is part of a highly conserved signaling platform that regulates the dimerization and activation of the ACE2 receptors and the Toll-like receptors (TLRs) implicated in the cytokine release syndrome (CRS). Activated Neu-1 cleaves glycosylated residues that provide a steric hindrance to both ACE2 and TLR dimerization, a process critical to both viral attachment to the receptor and entry into the cell and TLR activation. Blocking Neu-1 inhibited ACE2 receptor dimerization and internalization, TLR dimerization and activation, and the expression of several key inflammatory molecules implicated in the CRS and death from ARDS. Treatments that target Neu-1 are predicted to be highly effective against infection with SARS-CoV-2, given the central role played by this enzyme in viral cellular entry and the induction of the CRS.

Curcumin Efficacy in a Serum/Glucose Deprivation-Induced Neuronal PC12 Injury Model

BACKGROUND

Glucose/serum deprivation (GSD), has been used for understanding molecular mechanisms of neuronal damage during ischemia. It has been suggested that curcumin may improve neurodegenerative diseases.

AIM

In this study, the protective effects of curcumin and its underlying mechanisms were investigated in PC12 cells upon GSD-induced stress.

METHODS

PC12 cells were cultured in DMEM overnight and then incubated in GSD condition for either 6 or 12h. GSD-treated cells were pretreated with various concentrations of curcumin (10, 20, and 40 μM) for 5h. The cell viability, apoptosis, reactive oxygen species (ROS) level, oxidative stress, expression of apoptosis-related genes, and IL-6 were determined.

RESULTS

Curcumin increased cell viability and caused an anti-apoptotic effect in PC12 cells exposed for 12h to GSD . Curcumin also increased antioxidant enzyme expression, suppressed lipid peroxidation, and decreased interleukin-6 secretion in PC12 cells subjected to GSD. In addition, pretreatment with curcumin down-regulated pro-apoptotic (Bax), and up-regulated antiapoptotic (Bcl2) mediators.

CONCLUSION

Curcumin mitigates many of the adverse effects of ischemia, and therefore, should be considered as an adjunct therapy in ischemic patients.

Safranal protects against ischemia-induced PC12 cell injury through inhibiting oxidative stress and apoptosis

Safranal, isolated from saffron (Crocus sativus L.), is known to possesses neuroprotective effects. In this study, the neuroprotective potential of safranal against PC12 cell injury triggered by ischemia/reperfusion was investigated. PC12 cells were pretreated with safranal at concentration ranges of 10-160 μM for 2 h and then deprived from oxygen-glucose-serum for 6 h, followed by reoxygenation for 24 h (OGD condition). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), 2,7-dichlorofluorescin diacetate (DCF-DA), and comet assays were used to measure the extent of cellular viability, reactive oxygen substances (ROS), and DNA damage, respectively. Also, propidium iodide (PI) flow cytometry assay and western blotting of bax, bcl-2, and cleaved caspase-3 were performed for assessment of apoptosis. OGD exposure reduced the cell viability and increased intracellular ROS production, oxidative DNA damage, and apoptosis, in comparison with untreated control cells. Pretreatment with safranal (40 and 160 μM) significantly attenuated OGD-induced PC12 cell death, oxidative damage, and apoptosis. Furthermore, safranal markedly reduced the overexpression of bax/bcl-2 ratio and active caspase-3 following OGD (p < 0.05). The present findings indicated that safranal protects against OGD-induced neurotoxicity via modulating of oxidative and apoptotic responses.Graphical abstract The schematic representation of the mode of action of safranal against PC12 cells death induced by oxygen-glucose-serum deprivation and reoxygenation (OGD-R).

The mechanism of neuroprotective effect of Viola odorata against serum/glucose deprivation-induced PC12 cell death

Objective:

Oxidative stress is associated with the pathogenesis of brain ischemia and other neurodegenerative disorders. Previous researches have shown the antioxidant activity of Viola odorata L. In this project, we studied neuro-protective and reactive oxygen species (ROS) scavenging activities of methanol (MeOH) extract and other fractions isolated from V. odorata in PC12 cell line in serum/glucose deprivation (SGD) condition.

Materials and Methods:

The PC12 neuronal cells were pretreated for 6 hr with MeOH extract and fractions of V. odorata (1 to 25 μg/ml) followed by 24 hr incubation under SGD condition. Cell viability was measured by Alamar Blue^® assay. The level of ROS was calculated using DCFH-DA. Also, Bax/Bcl-2 protein ratio was analyzed by western blot assay.

Results:

SGD condition significantly decreased cells viability (p<0.001). Pretreatment with EtOAc (12.5 and 25 µg/ml), BuOH (12, 25, 50 µg/ml) and CH₂Cl₂ (1.5 µg/ml) fractions of V. odorata reduced SGD-induced cytotoxicity. MeOH extract could not increase the viability significantly. All four semi polar fractions (EtOAc, BuOH, CH2Cl2 and MeOH) decreased SGD-induced ROS production and changed Bax/Bcl-2 ratio.

Conclusion:

V. odorata showed promising effects against SGD condition; further mechanistic and clinical studies are warranted before application of V. odorata as a neuro-protective agent.

HIV-1 Tat protein promotes neuronal dysregulation by inhibiting E2F transcription factor 3 (E2F3)

Individuals who are infected with HIV-1 accumulate damage to cells and tissues (e.g. neurons) that are not directly infected by the virus. These include changes known as HIV-associated neurodegenerative disorder (HAND), leading to the loss of neuronal functions, including synaptic long-term potentiation (LTP). Several mechanisms have been proposed for HAND, including direct effects of viral proteins such as the Tat protein. Searching for the mechanisms involved, we found here that HIV-1 Tat inhibits E2F transcription factor 3 (E2F3), CAMP-responsive element-binding protein (CREB), and brain-derived neurotropic factor (BDNF) by up-regulating the microRNA miR-34a. These changes rendered murine neurons dysfunctional by promoting neurite retraction, and we also demonstrate that E2F3 is a specific target of miR-34a. Interestingly, bioinformatics analysis revealed the presence of an E2F3-binding site within the CREB promoter, which we validated with ChIP and transient transfection assays. Of note, luciferase reporter assays revealed that E2F3 up-regulates CREB expression and that Tat interferes with this up-regulation. Further, we show that miR-34a inhibition or E2F3 overexpression neutralizes Tat's effects and restores normal distribution of the synaptic protein synaptophysin, confirming that Tat alters these factors, leading to neurite retraction inhibition. Our results suggest that E2F3 is a key player in neuronal functions and may represent a good target for preventing the development of HAND.

Agonist-Biased Signaling via Matrix Metalloproteinase-9 Promotes Extracellular Matrix Remodeling

The extracellular matrix (ECM) is a highly dynamic noncellular structure that is crucial for maintaining tissue architecture and homeostasis. The dynamic nature of the ECM undergoes constant remodeling in response to stressors, tissue needs, and biochemical signals that are mediated primarily by matrix metalloproteinases (MMPs), which work to degrade and build up the ECM. Research on MMP-9 has demonstrated that this proteinase exists on the cell surface of many cell types in complex with G protein-coupled receptors (GPCRs), and receptor tyrosine kinases (RTKs) or Toll-like receptors (TLRs). Through a novel yet ubiquitous signaling platform, MMP-9 is found to play a crucial role not only in the direct remodeling of the ECM but also in the transactivation of associated receptors to mediate and recruit additional remodeling proteins. Here, we summarize the role of MMP-9 as it exists in a tripartite complex on the cell surface and discuss how its association with each of the TrkA receptor, Toll-like receptors, epidermal growth factor receptor, and the insulin receptor contributes to various aspects of ECM remodeling.

Protective effects of glucosamine and its acetylated derivative on serum/glucose deprivation-induced PC12 cells death: Role of reactive oxygen species

Finding products with antiapoptotic activities has been one of the approaches for the treatment of neurodegenerative disorders. Serum/glucose deprivation (SGD) has been used as a model for the investigation of the molecular mechanisms of neuronal ischemia. Recent studies indicated that glucosamine (GlcN) and N-acetyl glucosamine (GlcNAc) have many pharmacological effects including antioxidant activities. The present study aimed to investigate the protective effects of GlcN and GlcNAc against SGD-induced PC12 cells injury. The PC12 cells were pretreated with GlcN and GlcNAc for 2 h, and then exposed to SGD for 6, 12 and 24 h. Cell viability was evaluated by MTT assay. The level of intracellular reactive oxygen species (ROS) was determined by flow cytometry using 2',7'- dichlorofluorescin diacetate (DCFH-DA) as a probe. SGD condition caused a significant reduction in cell survival after 6, 12, and 24 h (P < 0.001). Pretreatment with GlcN and GlcNAc (0.6-20 mM) increased cell viability following SGD insult. A significant increase in cell apoptosis was observed in cells under SGD condition after 12 h (P < 0.001). Pretreatment with GlcN and GlcNAc (5-20 mM) decreased apoptosis following SGD condition after 12 h. SGD resulted in a significant increase in intracellular ROS production after 12 h. Pretreatment with both amino sugars at concentrations of 10 to 20 mM could reverse the ROS increment. Results indicated that GlcN and GlcNAc had a cytoprotective property against SGD-induced cell death via anti-apoptosis and antioxidant activities, suggesting that these aminosugers have the potential to be used as novel therapeutic agents for neurodegenerative disorders.

Trypanosoma cruzi Trans-sialidase: structural features and biological implications

Trypanosoma cruzi trans-sialidase (TcTS) has intrigued researchers all over the world since it was shown that T. cruzi incorporates sialic acid through a mechanism independent of sialyltransferases. The enzyme has being involved in a vast myriad of functions in the biology of the parasite and in the pathology of Chagas' disease. At the structural level experiments trapping the intermediate with fluorosugars followed by peptide mapping, X-ray crystallography, molecular modeling and magnetic nuclear resonance have opened up a three-dimensional understanding of the way this enzyme works. Herein we review the multiple biological roles of TcTS and the structural studies that are slowly revealing the secrets underlining an efficient sugar transfer activity rather than simple hydrolysis by TcTS.

Characterizing the cytoprotective activity of Sarracenia purpurea L., a medicinal plant that inhibits glucotoxicity in PC12 cells

BACKGROUND

The purple pitcher plant, Sarracenia purpurea L., is a widely distributed species in North America with a history of use as both a marketed pain therapy and a traditional medicine in many aboriginal communities. Among the Cree of Eeyou Istchee in northern Québec, the plant is employed to treat symptoms of diabetes and the leaf extract demonstrates multiple anti-diabetic activities including cytoprotection in an in vitro model of diabetic neuropathy. The current study aimed to further investigate this activity by identifying the plant parts and secondary metabolites that contribute to these cytoprotective effects.

METHODS

Ethanolic extracts of S. purpurea leaves and roots were separately administered to PC12 cells exposed to glucose toxicity with subsequent assessment by two cell viability assays. Assay-guided fractionation of the active extract and fractions was then conducted to identify active principles. Using high pressure liquid chromatography together with mass spectrometry, the presence of identified actives in both leaf and root extracts were determined.

RESULTS

The leaf extract, but not that of the root, prevented glucose-mediated cell loss in a concentration-dependent manner. Several fractions elicited protective effects, indicative of multiple active metabolites, and, following subfractionation of the polar fraction, hyperoside (quercetin-3-O-galactoside) and morroniside were isolated as active constituents. Phytochemical analysis confirmed the presence of hyperoside in the leaf but not root extract and, although morroniside was detected in both organs, its concentration was seven times higher in the leaf.

CONCLUSION

Our results not only support further study into the therapeutic potential and safety of S. purpurea as an alternative and complementary treatment for diabetic complications associated with glucose toxicity but also identify active principles that can be used for purposes of standardization and quality control.

Protective Effect of Scutellaria litwinowii Extract on Serum/Glucose-Deprived Cultured PC12 Cells and Determining the Role of Reactive Oxygen Species

Considering the wide, positive reporting of the role of reactive oxygen species in ischemic brain injury, searching for antioxidant drugs within herbal remedies is logical. In this study, the protective effects of Scutellaria litwinowii Bornm. & Sint. on cell viability and reactive oxygen species production in cultured PC12 cells were investigated under serum/glucose-deprivation-induced cell death. After cells were seeded overnight, they were then deprived of serum/glucose for 24 h. Cells were treated with different concentrations of S. litwinowii extract (7.75–250 μg/mL). Cell viability was quantitated by MTT assay, and intracellular reactive oxygen species production was measured by flow cytometry. Serum/glucose-deprivation induced significant cell death after 24 h (P < 0.001). Treatment with S. litwinowii (7.75–250 μg/mL) reduced serum/glucose deprivation-induced cytotoxicity in PC12 cells after 24 h. A significant increase in intracellular reactive oxygen species production was seen following serum/glucose deprivation (P < 0.001). S. litwinowii (62 and 125 μg/mL, P < 0.01) treatment reversed the increased reactive oxygen species production following ischemic insult. This demonstrates that S. litwinowii extract protects PC12 cells against serum/glucose-deprivation-induced cell death by antioxidant mechanisms, which indicates the potential therapeutic application of S. litwinowii in managing cerebral ischemic and neurodegenerative disorders.

Infusion of BDNF into the nucleus accumbens of aged rats improves cognition and structural synaptic plasticity through PI3K-ILK-Akt signaling

To investigate the involvement of the nucleus accumbens (NAc) in cognitive impairment and the therapeutic effects of brain-derived neurotrophic factor (BDNF) in an animal model of cognitive deficit, we infused BDNF into the NAc of cognitively impaired aged rats. Cognition was evaluated by Morris water maze test. Structural synaptic plasticity was measured by Golgi staining. Brain tissue homogenization was used to measure the changes in signal molecules. Cultured PC-12 cells expressing tyrosine kinase receptor (Trk) B/p75 neurotrophin receptor (p75(NTR)), p75(NTR) or TrkA/p75(NTR) receptors were used for BDNF stimulation assays. Significant decreases in the levels of BDNF, phosphatidylinositol-3-kinase (PI3K) and integrin-linked kinase (ILK) activity, protein kinase B (Akt) Ser⁴⁷³ phosphorylation, dendritic branching, and density of dendritic spines on medium spiny neurons were observed in the NAc. Importantly, infusion of BDNF restored cognition, synaptic plasticity, and cell signaling. In cultured PC-12 cells, BDNF activated PI3K/Akt signaling through the TrkB receptor, whereas stimulation of ILK/Akt occurred through TrkA/p75(NTR) heteroreceptor. Our study suggested that the decreased BDNF level and its downstream signaling as well as loss of synaptic plasticity in the NAc are associated with cognitive impairments in aged rats. The BDNF-activated PI3K-Akt and ILK-Akt signaling play a key role in structural synaptic plasticity. Our study also suggested that BDNF could be a mechanism-based treatment for dementia.

Neurodegeneration and neuroregeneration in Chagas disease

Autonomic dysfunction plays a significant role in the development of chronic Chagas disease (CD). Destruction of cardiac parasympathetic ganglia can underlie arrhythmia and heart failure, while lesions of enteric neurons in the intestinal plexuses are a direct cause of aperistalsis and megasyndromes. Neuropathology is generated by acute infection when the parasite, though not directly damaging to neuronal cells, elicits immune reactions that can become cytotoxic, inducing oxidative stress and neurodegeneration. Anti-neuronal autoimmunity may further contribute to neuropathology. Much less clear is the mechanism of subsequent neuronal regeneration in patients that survive acute infection. Morphological and functional recovery of the peripheral neurons in these patients correlates with the absence of CD clinical symptoms, while persistent neuronal deficiency is observed for the symptomatic group. The discovery that Trypanosoma cruzi trans-sialidase can moonlight as a parasite-derived neurotrophic factor (PDNF) suggests that the parasite might influence the balance between neuronal degeneration and regeneration. PDNF functionally mimics mammalian neurotrophic factors in that it binds and activates neurotrophin Trk tyrosine kinase receptors, a mechanism which prevents neurodegeneration. PDNF binding to Trk receptors triggers PI3K/Akt/GSK-3β and MAPK/Erk/CREB signalling cascades which in neurons translates into resistance to oxidative and nutritional stress, and inhibition of apoptosis, whereas in the cytoplasm of infected cells, PDNF represents a substrate-activator of the host Akt kinase, enhancing host-cell survival until completion of the intracellular cycle of the parasite. Such dual activity of PDNF provides sustained activation of survival mechanisms which, while prolonging parasite persistence in host tissues, can underlie distinct outcomes of CD.

Protective Action of Neurotrophic Factors and Estrogen against Oxidative Stress-Mediated Neurodegeneration

Oxidative stress is involved in the pathogenesis of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. Low levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are important for maintenance of neuronal function, though elevated levels lead to neuronal cell death. A complex series of events including excitotoxicity, Ca(2+) overload, and mitochondrial dysfunction contributes to oxidative stress-mediated neurodegeneration. As expected, many antioxidants like phytochemicals and vitamins are known to reduce oxidative toxicity. Additionally, growing evidence indicates that neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and estrogens significantly prevent neuronal damage caused by oxidative stress. Here, we review and discuss recent studies addressing the protective mechanisms of neurotrophic factors and estrogen within this system.

Protective effect of Nigella sativa extract and thymoquinone on serum/glucose deprivation-induced PC12 cells death

The serum/glucose deprivation (SGD)-induced cell death in cultured PC12 cells represents a useful in vitro model for the study of brain ischemia and neurodegenerative disorders. Nigella sativa L. (family Ranunculaceae) and its active component thymoquinone (TQ) has been known as a source of antioxidants. In the present study, the protective effects of N. sativa and TQ on cell viability and reactive oxygen species (ROS) production in cultured PC12 cells were investigated under SGD conditions. PC12 cells were cultured in DMEM medium containing 10% (v/v) fetal bovine serum, 100 units/ml penicillin, and 100 microg/ml streptomycin. Cells were seeded overnight and then deprived of serum/glucose for 6 and 18 h. Cells were pretreated with different concentrations of N. sativa extract (15.62-250 microg/ml) and TQ (1.17-150 microM) for 2 h. Cell viability was quantitated by MTT assay. Intracellular ROS production was measured by flow cytometry using 2',7'-dichlorofluorescin diacetate (DCF-DA) as a probe. SGD induced significant cells toxicity after 6, 18, or 24 h (P < 0.001). Pretreatment with N. sativa (15.62-250 microg/ml) and TQ (1.17-37.5 microM) reduced SGD-induced cytotoxicity in PC12 cells after 6 and 18 h. A significant increase in intracellular ROS production was seen following SGD (P < 0.001). N. sativa (250 microg/ml, P < 0.01) and TQ (2.34, 4.68, 9.37 microM, P < 0.01) pretreatment reversed the increased ROS production following ischemic insult. The experimental results suggest that N. sativa extract and TQ protects the PC12 cells against SGD-induced cytotoxicity via antioxidant mechanisms. Our findings might raise the possibility of potential therapeutic application of N. sativa extract and TQ for managing cerebral ischemic and neurodegenerative disorders.

Dependence of pathogen molecule-induced toll-like receptor activation and cell function on Neu1 sialidase

The signaling pathways of mammalian Toll-like receptors (TLR) are well characterized, but the initial molecular mechanisms activated following ligand interactions with the receptors remain poorly defined. Here, we show a membrane controlling mechanism that is initiated by ligand binding to TLR-2, -3 and-4 to induce Neu1 sialidase activity within minutes in live primary bone marrow (BM) macrophage cells and macrophage and dendritic cell lines. Central to this process is that Neu1 and not Neu2,-3 and-4 forms a complex with TLR-2,-3 and-4 on the cell surface of naïve macrophage cells. Neuraminidase inhibitors BCX1827, 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (DANA), zanamivir and oseltamivir carboxylate have a limited significant inhibition of the LPS-induced sialidase activity in live BMC-2 macrophage cells but Tamiflu (oseltamivir phosphate) completely blocks this activity. Tamiflu inhibits LPS-induced sialidase activity in live BMC-2 cells with an IC(50) of 1.2 microM compared to an IC(50) of 1015 microM for its hydrolytic metabolite oseltamivir carboxylate. Tamiflu blockage of LPS-induced Neu1 sialidase activity is not affected in BMC-2 cells pretreated with anticarboxylesterase agent clopidogrel. Endotoxin LPS binding to TLR4 induces Neu1 with subsequent activation of NFkappaB and the production of nitric oxide and pro-inflammatory IL-6 and TNFalpha cytokines in primary and macrophage cell lines. Hypomorphic cathepsin A mice with a secondary Neu1 deficiency respond poorly to LPS-induced pro-inflammatory cytokines compared to the wild-type or hypomorphic cathepsin A with normal Neu1 mice. Our findings establish an unprecedented mechanism for pathogen molecule-induced TLR activation and cell function, which is critically dependent on Neu1 sialidase activity associated with TLR ligand treated live primary macrophage cells and macrophage and dendritic cell lines.

Trypanosoma cruzi-Derived Neurotrophic Factor: Role in Neural Repair and Neuroprotection

Some patients infected with the parasite Try-panosoma cruzi develop chronic Chagas' disease, while others remain asymptomatic for life. Although pathological mechanisms that govern disease progression remain unclear, the balance between degeneration and regeneration in the peripheral nervous system seems to contribute to the different clinical outcomes. This review focuses on certain new aspects of host-parasite interactions related to regeneration in the host nervous system induced by the trans-sialidase of T. cruzi, also known as a parasite-derived neurotrophic factor (PDNF). PDNF plays multiple roles in T. cruzi infection, ranging from immunosuppression to functional mimicry of mammalian neurotrophic factors and inhibition of apoptosis. PDNF affinity to neurotrophin Trk receptors provide sustained activation of cellular survival mechanisms resulting in neuroprotection and neuronal repair, resistance to cytotoxic insults and enhancement of neuritogenesis. Such unique PDNF-elicited regenerative responses likely prolong parasite persistence in infected tissues while reducing neuropathology in Chagas' disease.

Trypanosoma cruzi promotes neuronal and glial cell survival through the neurotrophic receptor TrkC

Trypanosoma cruzi, the agent of Chagas' disease, promotes neuron survival through receptor tyrosine kinase TrkA and glycosylphosphatidylinositol-anchored glial cell-derived family ligand receptors (GFRalpha). However, these receptors are expressed by only a subset of neurons and at low levels or not at all in glial cells. Thus, T. cruzi might exploit an additional neurotrophic receptor(s) to maximize host-parasite equilibrium in the nervous system. We show here that T. cruzi binds TrkC, a neurotrophic receptor expressed by glial cells and many types of neurons, and that the binding is specifically inhibited by neurotrophin-3, the natural TrkC ligand. Coimmunoprecipitation and competition assays show that the trans-sialidase/parasite-derived neurotrophic factor (PDNF), previously identified as a TrkA ligand, mediates the T. cruzi-TrkC interaction. PDNF promotes TrkC-dependent mitogen-activated protein kinase signaling, neurite outgrowth, and survival of genetically engineered PC12 neuronal cells and glial Schwann cells in a TrkC-dependent manner. Thus, TrkC is a new neurotrophic receptor that T. cruzi engages to promote the survival of neuronal and glial cells. The results raise the possibility that T. cruzi recognition of TrkC underlies regenerative events in nervous tissues of patients with Chagas' disease.

Neuroprotective effects of salidroside in the PC12 cell model exposed to hypoglycemia and serum limitation

The hypoglycemia and serum limitation-induced cell death in cultured PC12 cells represents a useful in vitro model for the study of brain ischemia and neurodegenerative disorders. Salidroside is a phenylpropanoid glycoside isolated from Rhodiola rosea L., a traditional Chinese medicinal plant, and has displayed a broad spectrum of pharmacological properties. In this study, MTT assay, Hoechst 33342 staining, and flow cytometry with annexin V/PI staining collectively showed that pretreatment with salidroside attenuated, in a dose-dependent manner, cell viability loss, and apoptotic cell death in cultured PC12 cells induced by hypoglycemia and serum limitation. RT-PCR, Western blot analysis, and enzymatic colorimetric assay indicated the changes in expression levels of Bcl-2, Bax, and caspase3 in PC12 cells on exposure to hypoglycemia and serum limitation with and without salidroside pretreatment, respectively. Rhodamine 123 staining and flow cytometry with 2',7'-Dichlorofluorescin diacetate staining revealed the changes in the mitochondrial membrane potential and radical oxygen species (ROS) production in PC12 cells on exposure to hypoglycemia and serum limitation with and without salidroside pretreatment, respectively. The experimental results suggest that salidroside protects the PC12 cells against hypoglycemia and serum limitation-induced cytotoxicity possibly by the way of the modulation of apoptosis-related gene expression, the restoration of the mitochondrial membrane potential, and the inhibition of the intracellular ROS production. Our findings might raise a possibility of potential therapeutic applications of salidroside for preventing and treating cerebral ischemic and neurodegenerative diseases.

Chagas' disease parasite-derived neurotrophic factor activates cholinergic gene expression in neuronal PC12 cells

A parasite-derived neurotrophic factor (PDNF) produced by the Chagas' disease parasite Trypanosoma cruzi binds nerve growth factor (NGF) receptor TrkA, increasing receptor autophosphorylation, and activating phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK/Erk) pathways, and transcription factor CREB. The end-result is enhanced survival and neuritogenesis of various types of neurons. PDNF also enhances the expression and activity of tyrosine hydroxylase, a rate limiting enzyme in the synthesis of dopamine and other catecholamine neurotransmitters. It remains unknown, however, if PDNF alters expression and metabolism of acetylcholine (ACh), a neurotransmitter thought to play a role in Chagas' disease progression. Here we demonstrate that PDNF stimulates mRNA and protein expression of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT), which are critical for synthesis and storage of ACh. Stimulation requires functional TrkA because it did not occur in cell mutants that lack the receptor and in TrkA-expressing wild-type cells treated with K252a, an inhibitor of TrkA kinase activity. It also requires TrkA-dependent PI3K and MAPK/Erk signaling pathways because PDNF stimulation of cholinergic transcripts is abolished by specific pharmacological inhibitors. Furthermore, the cholinergic actions of PDNF were reproduced by PDNF-expressing extracellular T. cruzi trypomastigotes at the start of host cell invasion. In contrast, host cells bearing intracellular T. cruzi showed decreased, rather than increased, cholinergic gene expression. These results suggest that T. cruzi invasion of the nervous system alters cholinergic gene expression and that could play a role in neuropathology, and/or lack thereof, in Chagas' disease patients.